Conventional spring blinds are provided with a so-called hollow keyway tube, onto which one end of suitable blind fabric or other material is attached, the remainder of the material being wrapped or rolled around the periphery of the tube. A spring mechanism is provided within the hollow tube, which is itself supported between suitable brackets. The blind fabric may be caused to unroll for any desired length (up to the limit of material rolled on the tube), usually by pulling on it, which causes the tube to rotate about its axis, thereby winding up (ie further tensioning) the spring mechanism. In a conventional, free-hanging blind, a locking means is also provided which prevents the spring from unwinding by itself. However, upon releasing the spring mechanism, the tube is able to re-roll the unfurled material back up onto itself.
Such an arrangement is particularly suitable for vertically hung blinds, although the same principles may be applied in other situations where a cover (eg swimming pool cover) or awning is required to extend over a specified area. However, where the blind or cover is not vertically hung, it will generally be found that the locking to secure the blind against re-rolling means (usually in the form of pins which act gravity) is not needed as the blind itself will be preferably held taught by means of some suitable arrangement such as a hook or catch arrangement.
In such situations however, especially in horizontal arrangements such as pool covers or external awnings, there is a limit to the useful span of cover which could be conveniently achieved (ie considering the length of material which may be unrolled), requiring larger spring mechanisms to accommodate increasing lengths of material to be extended and rewound. This of course means increasing difficulty of operation, as it becomes necessary to pull against the increasing tension of larger springs over increasing lengths of material required to be unrolled. Hence there are no known solutions for covering larger expanses.